1. Field of the Invention
The present invention relates to a piezoelectric device, and more particularly, to a piezoelectric device having a structure resistant to external physical or mechanical shocks and a method for manufacturing the same, and a driven assembly with the piezoelectric device.
2. Description of the Related Art
A piezoelectric device can generate a mechanical displacement according to structural deformation caused by a dipole formed inside ceramic due to an electric field between two electrodes when a voltage is applied from the outside. The piezoelectric device is mainly used in various types of actuator applications that should use a displacement. For example, the actuator applications may be a fuel injector, a nano-positioning system, an inkjet head, etc.
Since the displacement of the piezoelectric device increases in proportion to the electric field, a higher voltage should be applied between the electrodes to obtain a larger displacement. However, generation of a high voltage as an operating voltage may cause a huge problem in circuits. Thus, usually, a piezoelectric material is implemented in the form of a multilayer structure in which the thickness between electrodes is reduced to generate a large displacement through a higher electric field even in a low voltage. For example, when the same voltage is applied to a multilayer piezoelectric material having nine layers and a single-layer piezoelectric material, an electric field applied to the multilayer piezoelectric material can generate a displacement nine times larger than that of the single-layer piezoelectric material.
Meanwhile, ultrahigh multilayer piezoelectric actuators such as a fuel injector and a nano-positioning system are all exposed to physical and mechanical shocks, and most of the damages due to the physical or mechanical shocks are concentrated on the coupling portion between a polycrystalline piezoelectric material and an external connection member connected thereto. However, since the polycrystalline piezoelectric material itself is vulnerable to external shocks, it is very difficult to implement a piezoelectric device that is resistant to external shocks.